Mankotia, S. | Search bioRxiv

bioRxiv2024

ELONGATED HYPOCOTYL 5 (HY5) and POPEYE (PYE) Regulate Intercellular Iron Transport in Plants.

Plants maintain iron (Fe) homeostasis under varying environmental conditions by balancing processes such as Fe uptake, transport, and storage. In Arabidopsis, POPEYE (PYE), a basic helix-loop-helix (bHLH) transcription factor (TF), has been shown to play a crucial role in regulating this balance. In recent years, the mechanisms regulating Fe uptake have been well established but the upstream transcriptional regulators of Fe transport and storage are still poorly understood. In this study, we report that ELONGATED HYPOCOTYL5 (HY5), a basic leucine zipper (bZIP) TF which has recently been shown to play a crucial role in Fe homeostasis, interacts with PYE. Molecular, genetic and biochemical approaches revealed that PYE and HY5 have overlapping as well as some distinct roles in regulation of Fe deficiency response. We found that HY5 and PYE both act as a repressor of Fe transport genes such as YSL3, FRD3 NPF5.9, YSL2, NAS4, and OPT3. HY5 was found to directly bind on the promoter of these genes and regulate intercellular Fe transport. Further analysis revealed that HY5 and PYE directly interact at the same region on PYE and NAS4 promoter. Overall, this study revealed that HY5 regulates Fe homeostasis by physically interacting with PYE as well as independently.

plant biology↗

bioRxiv2022

Elongated Hypocotyl 5 (HY5) regulates BRUTUS (BTS) to maintain Iron homeostasis in Arabidopsis thaliana.

Iron (Fe) is an essential micronutrient for both plants and animals. Fe limitation significantly reduces crop yield and therefore has adverse impacts on human nutrition. Owing to limited bioavailability of Fe, plants have adapted different strategies that regulate Fe uptake and homeostasis. Particularly, modifications of root growth traits are a key for the survival of plants on Fe-deficient soils. Understanding the molecular basis for these root growth responses will have critical implications for plant breeding. Fe uptake is regulated by a cascade of basic helix-loop-helix (bHLH) transcription factors. In our study, we show that HY5 (Elongated Hypocotyl 5), a member of the basic leucine zipper (bZIP) family of transcription factors plays an important role in the Fe deficiency signalling pathway in Arabidopsis thaliana. The hy5 mutant plants failed to mount an optimum Fe deficiency response and showed severe root growth defects under Fe limitation that could be partially reverted by complementation of hy5 mutant. qRT-PCR analysis revealed that the induction of the genes involved in Fe uptake pathway [FER-like iron deficiency-induced transcription factor (FIT), Ferric Reduction Oxidase 2 (FRO2) and Iron-Regulated Transporter1 (IRT1)] is significantly reduced in the hy5 mutants as compared to the wild-type plants under Fe deficiency. Moreover, we also found that HY5 function is critical for activating the expression of coumarin biosynthesis genes (F6H1, S8H, PDR9 and BGLU42) under Fe deficiency. Interestingly, our results showed that HY5 acts as a negative regulator of BRUTUS (BTS) which is known to negatively regulate Fe deficiency response. Chromatin Immunoprecipitation followed by qPCR revealed direct binding of HY5 to the promoter of BTS. Altogether, our results showed that HY5 plays an important role in regulation of Fe deficiency responses in Arabidopsis.

plant biology↗